Set Appliance State:

Mains Power Off
Gas Off
Main On/Off Control in the On position
Heating Control to Heating & Hot Water
CH Temperature Control To Maximum
Remove the spark igniter cap and wedge in place below
the igniter against the heat exchanger as shown
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Watch for sparking from the igniter lead to the heat exchanger case.
Note.
Ensure the electrode lead is placed close to the heat exchanger casing for sparking to occur. Keep clear of the sparking electrode lead.